added format_currency and added options to all currency fields

stock/doctype/item/item.txt

@@ -2,7 +2,7 @@
  {
   "creation": "2013-01-21 18:19:22", 
   "docstatus": 0, 
-  "modified": "2013-01-22 14:47:00", 
+  "modified": "2013-01-23 17:00:07", 
   "modified_by": "Administrator", 
   "owner": "Administrator"
  }, 
@@ -381,7 +381,7 @@
   "description": "Buying Cost will be updated from Purchase Orders and Purchase Receipts. <br>The buying cost will calculated by moving average method.", 
   "doctype": "DocField", 
   "fieldname": "buying_cost", 
-  "fieldtype": "Currency", 
+  "fieldtype": "Float", 
   "label": "Buying Cost", 
   "no_copy": 1, 
   "oldfieldname": "buying_cost", 
@@ -392,7 +392,7 @@
   "depends_on": "eval:doc.is_purchase_item==\"Yes\"", 
   "doctype": "DocField", 
   "fieldname": "last_purchase_rate", 
-  "fieldtype": "Currency", 
+  "fieldtype": "Float", 
   "label": "Last Purchase Rate", 
   "no_copy": 1, 
   "oldfieldname": "last_purchase_rate", 
@@ -403,7 +403,7 @@
   "depends_on": "eval:doc.is_purchase_item==\"Yes\"", 
   "doctype": "DocField", 
   "fieldname": "standard_rate", 
-  "fieldtype": "Currency", 
+  "fieldtype": "Float", 
   "label": "Standard Rate", 
   "oldfieldname": "standard_rate", 
   "oldfieldtype": "Currency"
@@ -525,7 +525,7 @@
   "depends_on": "eval:doc.is_sales_item==\"Yes\"", 
   "doctype": "DocField", 
   "fieldname": "sales_rate", 
-  "fieldtype": "Currency", 
+  "fieldtype": "Float", 
   "hidden": 1, 
   "label": "Sales Rate", 
   "oldfieldname": "sales_rate",